As far as the lubricating system of automobile is concerned, the general knowledge is that the friction in the cylinder would bring about the penetration of the fine iron particles into the lubricating oil. The failure to defecate the unexpected fine iron particles would be followed by the incomplete combustion of the fuel in the cylinder and further the leakage of combustioned air. A conventional method to solve this problem is to provide an oil filter device for the purpose of filtering the circulated lubricating oil in the lubricating system. However, the conventional lubricating oil filter device only teaches the application of a rolled paper filter coaxial in relation to the main body of the lubricating oil filter device. The rolled paper filter is provided between the main body thereof and a magnet which is provided within the main body. When the filtering of lubricating oil is in progress, the lubricating oil flows into the oil passage provided between the rolled paper filter and the main body thereof. Then, the lubricating oil flows outside from the outlet of the oil filter device. Due to the fact that the lubricating oil passes at first through the rolled paper filter during filtering, the fine iron particles would have an ill effect on the paper filter. Further due to the fact that the magnet is attached on to the inner wall of the paper filter and the passage for the lubricating oil to flow is not spacious, the more the fine iron particles are attracted on to the magnet, the less would be the capacity of the lubricating oil filter device. Besides, the accumulated fine iron particles would be peeled off in masses by the oil current and delivered to the engine. Hence, more damages may occur if this device has been in use for a long time. Therefore, the conventional lubricating oil filter device has still some defects and must be improved accordingly. It is the main object of this invention to improve the above defect, and furthermore to a new device of lubricating oil filter for practical use.